1. Field of the Invention
The present invention relates generally to gas turbine engines and, more particularly, to an expansion joint for use in connecting fluid piping of gas turbine engines.
2. Related Art
Gas turbine engines such as those used for aircraft propulsion necessarily include external piping systems for delivering fluids, either gases or liquids, from one engine component to another or for connecting an engine component with an aircraft system. These piping systems may necessarily be relatively long in length. An example of such a piping system is that which supplies cooling or heating air, depending upon engine condition, from a compressor stage of the core engine to a turbine component. External piping systems are typically fixedly mounted at opposite ends to stationary engine structures and, depending on engine condition, may be either hotter or cooler than adjacent engine structures. Consequently, piping systems may experience a differential thermal growth relative to that of the engine between points of attachment of the piping system. Accordingly, such piping systems typically include at least one expansion joint connecting adjacent fluid-carrying pipes to accommodate differential thermal expansion or contraction of the fluid-carrying pipes relative to the corresponding engine structure to which the pipes are attached.
One prior expansion joint is the piston seal type joint wherein an outer surface of a first fluid-carrying pipe slidingly engages an internal surface of an adjacent fluid-carrying pipe. Piston seal joints may accommodate expansion or contraction of one pipe relative to the other in a direction parallel to the longitudinal centerline of the joint and may further accommodate rotation of one pipe relative to the other about the joint centerline. However, piston seal joints are not tolerant of lateral misalignment which occurs when the centerlines of the mating pipes are generally parallel but laterally displaced relative to one another. Additionally, if the outer surface of the first pipe and the internal surface of the second pipe are cylindrical, the piston seal joint is also not tolerant of angular misalignment which occurs when the centerlines of the pipes are angled relative to one another. Furthermore, piston seal joints are subject to leakage due to a required clearance between the mating surfaces, manufacturing tolerances resulting in a larger than required clearance between the mating surfaces, and vibration induced wear on the mating surfaces. Although such joints may utilize wear coatings on the mating surfaces and/or vibration damping means to minimize leakage between the mating surfaces, this leakage may not be entirely eliminated. Accordingly, piston seal joints may not be suitable for use in piping systems transporting liquids such as fuel and oil where leaks may not be tolerated, unless other measures are employed to contain the leaks. When used in piping systems transporting gases, piston joint leaks may result in an engine performance penalty.
Another prior expansion joint is the bellows joint wherein an annular bellows extends between adjacent fluid-carrying pipes. The bellows joint is considered to be a zero leak joint and can accommodate relative expansion and contraction between the adjacent pipes. In order to avoid flow-induced high cycle fatigue failure in the bellows, the bellows joint typically includes a flow liner to shield the bellows undulations from the fluid flowpath. An example of such a bellows-type expansion joint is that which is disclosed in U.S. Pat. No. 5,145,215 to Udell, issued Sep. 8, 1992. As shown in FIGS. 1-5 the Udell joint does not include a constant diameter flow passage but instead has an inner sleeve 17 inserted within a larger outer sleeve 16. The cylindrical portion of sleeve 17 which mates with sleeve 16 is shown to be reduced in diameter relative to the enlarged inlet portion 18 of sleeve 17. The configuration of sleeve 17 causes a fluid system pressure drop relative to a joint having a flow passage with a constant flow area equal to that existing in enlarged inlet portion 18. Additionally, bellows-type expansion joints such as that disclosed in Udell are flow-direction sensitive. If the expansion joint is installed in the wrong direction fluid flow may be forced into the annular space between sleeve members, such as through gaps 29a, 29b, 30a and 30b illustrated in FIG. 2a of Udell, which in turn may cause excessive pressure drop and may lead to bellows damage. The Udell apparatus is configured to allow the smaller inner sleeve 17 to be cocked relative to the larger outer sleeve 16 as shown in FIG. 5 to absorb bending forces encountered in normal use. A limited cocking of sleeve members relative to one another, to accommodate bending forces incurred during use as described in Udell, or to accommodate angular misalignment at assembly between mating fluid pipes to which the expansion joint is connected, is desirable. However, bellows-type expansion joints of the general type having a smaller flow liner inserted into a larger mating coupling, wherein the flow liner and mating coupling may be angularly misaligned relative to one another, have been known to be subject to excessive misalignment causing high bending stresses in localized areas of the bellows.
Other problems which have been encountered with prior bellows-type expansion joints is bellows damage, particularly during assembly, due to excessive compression of the bellows and bellows distress caused by torsional loading of the bellows.
In view of the foregoing, prior to the present invention a need existed for an improved expansion joint for use in fluid piping systems to resolve the aforementioned problems associated with prior expansion joints.